the Method of its Transmission. 



107 



in the Drechsel bottle F. The air passed through a tube 

 containing cotton- wool, and through a drying-tube T of 

 calcium chloride. The central rod was made of three remov- 

 able parts BC, CD, DE, screwed together. After exposure 



ffiffTH _0 



Emanation Crs. ind£R 



Had. Cl 



for a known time in the presence of the emanation the rod 

 was removed, and the activity on the portion CD, length 15 

 cms., determined by the electrometer in the cylindrical testing 

 vessel L, shown in fig. 2 b. By this means the excited 



Fig 2 b. 



jc 



f fi 



ft 



etC 



ro- 



A -H 



£/)/}T/f 



r£ST/A/G CY/L/A/0£/? 



activity was determined on that portion of the rod where the 

 electric field was sensibly uniform. 



In most of the experiments the emanation was introduced 

 into the vessel A a day or two before observations were taken. 

 This ensured a uniform distribution of the emanation through- 

 out the cylinder by the process of diffusion. If observations 

 were required soon after the introduction of the emanation, 

 the emanation was uniformly mixed with the air by means of 

 a stirrer not shown in the figure. 



Some experiments were made with this apparatus on the 

 amount of excited activity on the central rod when positively 

 charged for different voltages. For the purpose of com- 

 parison, the results are expressed in terms of the percentage 

 amount on the same electrode exposed for the same time when 

 negatively charged with 300 volts between the electrodes. 

 The rod was exposed in the presence of the emanation for 

 15 minutes, then removed and a fresh rod introduced. In 



